1. Field of the Invention
The present invention relates to hydraulic valves, and more particularly to assemblies having a common monolithic block housing a plurality of individually operable valves.
2. Description of the Related Art
Construction equipment have movable members which are operated by hydraulic cylinder/piston arrangements and other types of hydraulic actuators and motors. For example, a mini-excavator has a boom that raises and lowers a bucket for moving dirt. The bucket can be replaced with other implements, either stationary or hydraulically powered. Hydraulic actuators are provided to raise and lower the boom and tilt the implement with respect to the boom. Separate hydraulic motors independently drive wheels or tracks on each side of the mini-excavator. Other hydraulic actuators position the boom relative to the mini-excavator cab and rotate the entire boom/cab structure about the drive wheels or tracks. A dozer blade is raised and lowered and the track width can be extended and retracted with other hydraulic circuits. An additional hydraulic circuit often is provided for auxiliary equipment. In total a mini-excavator may have nine or ten actuators.
The flow of fluid to and from each hydraulic actuator is typically controlled by a spool valve which is operated by a user manipulated lever or remote pilot circuit. The spool valve comprises a section of an assembly of all the hydraulic valves for the mini-excavator. Each valve section is formed by a separate body with the plurality of bodies bolted together to form the assembly. Depending on the particular hydraulic function being controlled, a given valve section may also have apertures for receiving pressure relief valves and a pressure compensating mechanism. The use of individual bodies offers the ability to assemble different types of valve sections according to the needs of the particular machine. One drawback of using a series of individual sections to form the valve assembly is the cost associated with machining the numerous faces, sealing grooves, and tie-bolt holes on each section, in addition to the assembly labor.
A common supply passage extends through the assembled sections furnishing pressurized hydraulic fluid to each spool valve, and a common return passage also is provided to return fluid from each valve to the tank of the hydraulic system. Movement of a spool of a valve opens and closes paths between the supply and return passages and the hydraulic actuator connected to workports of the associated valve section.
Because of the number of control devices that need to be connected to the valve assembly and the requirement that the body of each section within the assembly be able to withstand the pressures in the different passages, the size of each body resulted in a relatively large valve assembly. In mini-excavators, as well as hydraulic equipment in general, there is a desire to reduce the size of the valve assembly as much as possible. However incorporating multiple spool valves into a single-piece valve body often presents metal casting difficulties. Therefore, it is desirable to develop a body for housing a plurality of spool valves and other control devices in which the body can be cast as a single, monolithic, piece.